Pore pressure coefficient in frozen soils

The Skempton pore pressure coefficient,B, is defined as the variation in pore pressure with the unitchange in confining pressure under undrained conditions. TheBparameter is an essential parameter toconsider the coupled effects of solid–fluid compressibility and skeleton compressibility in a poroussystem. It is a key factor in exploring a possible definition of effective stress in frozen soil. However,limited experimental and theoretical research is available in the literature to give insight to the problem.Therefore, a series ofBtests on frozen clay was conducted in this study. Results from these tests, alongwith tests on Ottawa sand, as available in the literature, are analysed considering the effect of the icecrystallisation mode on the skeleton stiffness. The measuredBvalues were lower than expectedcompared withBvalues using models that consider single grain bulk stiffness. However, when thedifference in bulk stiffness of ice and that of soil grains is considered, even an increase in pore volume,for an increase in fluid pressure, at constant Terzaghi effective stress is possible. The‘pore stiffness’,which is different from the solid phase stiffness, can take a negative value and can be used to explain thelow measuredBvalues.